Automatic sensitivity adjustment in flash blindness protective device

ABSTRACT

Automatic sensitivity adjustment for day-night operation in flash blindness protective apparatus is obtained by supplying an electrical signal produced by a light detector in response to transient light through a differentiator circuit to a first comparator which provides an output signal if the differentiated electrical signal exceeds a first predetermined amplitude. If the electrical signal produced by the light detector in response to ambient light exceeds a predetermined maximum at a second comparator, the second comparator supplies an output signal to the first comparator to change the first predetermined amplitude to a second predetermined amplitude. An output signal from the first comparator initiates operation of eye protective measures. An interlock switching circuit provides protection from high voltages when the apparatus is not in use.

United States Patent Jekowski et al.

[451 Sept. 25, 1973 Inventors: Edward W. Jekowski, Brighton;

Kenneth J. Foster, Dedham, both of Mass.

Assignee: The United States of America as represented by the Secretaryof the NaVy, Washington, DC.

Filed: May 15, 1972 Appl. No.: 253,269

Durig 250/206 Kohler 250/229 Primary Examiner.lames W. LawrenceAssistant ExaminerD. C. Nelms Atr0rneyR. S. Sciascia et a1.

[57] ABSTRACT Automatic sensitivity adjustment for day-night operationin flash blindness protective apparatus is obtained by supplying anelectrical signal produced by a light detector in response to transientlight through a differentiator circuit to a first comparator whichprovides an output signal if the differentiated electrical signalexceeds a first predetermined amplitude. If the electrical signalproduced by the light detector in response to ambient light exceeds apredetermined maximum at a second comparator, the second comparatorsupplies an output signal to the first comparator to change the firstpredetermined amplitude to a second predetermined amplitude. An outputsignal from the first comparator initiates operation of eye protectivemeasures. An in terlock switching circuit provides protection from highvoltages when the apparatus is not in use.

10 Claims, 3 Drawing Figures [52] US. Cl. 250/209 R, 250/214 {51] Int.Cl. H0lj 39/12 [58] Field of Search 350/160, 269; 250/201, 206, 209,229, 214, 83.3; 315/149, 155,156, 157,158,159

[56] References Cited UNITED STATES PATENTS 3,389,259 6/1968 Zarem350/269 3,548,197 12/1970 Nordmann 350/269 3,321,630 5/1967 Durig250/209 +v WV '2 /7 t 20 z/ I vow/105 J, COMPARATOR mug, VOLTAGE IDFFEREN. COMPARATOR i TYATOR l/ w/ .5 T w n g i L l 50 PATENTED SEP 2 5I973 SHEET 3 [IF 3 1 AUTOMATIC SENSITIVITY ADJUSTMENT IN FLASH BLINDNESSPROTECTIVE DEVICE STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereof or therefor.

BACKGROUND OF THE INVENTION The present invention generally relates toautomatic switching systems and more particularly to their use in flashblindness protective systems for protecting the human eye from intenseflashes of light.

The intense flash of light emitted by a nuclear detonation can causeflash blindness or even retinal burns to an unprotected eye.Photocrhomic goggle systems have been developed with rapid response toprotect the eyes during such detonations. One such system is disclosedby Frederick E. Barstow et al. in U. S. Pat. No. 3,152,215 issued Oct.6, 1964. Prior systems, however, fail to take into account thedifference in protection needed during daytime and at night. At nightimethe dilation of the pupil is much greater than the daytime and anincrease in light'that would be relatively safe during the daytime couldcause severe problems to an eye adapted to the dark. Thus, prior systemsare set so that a certain intensity of light triggers a safety deviceand this level is low enough that an eye adapted for the nightime isprotected. However, systems set at such levels often trigger from anumber of false alarm sources in daytime when, in fact, such a thresholdlevel is not required to protect the eyes.

SUMMARY OF THE INVENTION determination supplies an output signal if theoutput of the sensor should exceed the maximum intensity permitted foreither the day or night mode of operation for which the light detectormodule is automatifally automatically This output of the light detectoris utilized to fire an electric flash circuit that renders photochromicgoggle lenses opaque. Thus, in one prior art electric flash system it isapplied to a spark gap trigger through a clamp circuit. The spark gaptrigger fires upon receipt of a signal from the light detector modulewhen the clamp circuit is in the unclamped condition. The output of thespark gap trigger fires a spark gap rendering it conductive. Thisenables the energy storage capacitors to operate the flash circuit. Theultraviolet light produced renders the photochromic lenses of thegoggles opaque. In addition, an interlock circuit provides protectionfrom high voltages and inhibits the light detector module from supplyingan output signal.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram of anapparatus incorporating the present invention;

FIG. 2 illustrates in schematic-block diagram form the present inventionin part in combination with a prior art electric flash system; and

FIG. 3 illustrates in schematic-block diagram form the interlock systemof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2,a light sensor 10 comprising a pair of identical photodiodes 11connected in parallel to allow overlap of their half power points supplyelectrical signals indicative of the light rays received. Generallyconsidered, photodiodes I] produce a signal having two parts, firstsignals representing transient light changes and a second signalrepresenting the ambient light level encountered. The light sensor 10 isphysically located in goggles 65 which are used in conjunction with ahelmet (not shown).

The electrical signals are supplied to a first comparator l2 anddifferentiator 13 within light detector system 16. Differentiator l3differentiates the first signal and ignores the second ambient signal.Differentiator 13 is band limited and may comprise an operationalamplifier circuit with both high and low bandpass filtering (not shown).Comparator 12 compares the second ambient signal from diodes 11 to avoltage reference +V and supplies an output signal to second comparator15 through diode 20 and resistor 21 if the second signal from diodes llexceeds a predetermined value indicating that the day threshold has beenexceeded and that detector system 16 is to be set for day operation. Thesignal from differentiator 13 is also applied to comparator 15. If theincoming second ambient signal from diodes ll fails to operatecomparator 12, then a signal +V, applied to comparator 15 throughresistor 17 determines the night time level that the output fromdifferentiator 13 must exceed to generate an output from comparator 15.If, however, comparator 12 is rendered operative a day time level takeseffect at comparator 15 that must be exceeded by the signal fromdifferentiator 13. This associated circuitry is set so that when thelight rate of rise exceeds 2.3 [LW/Cm /ILS (night threshold) or 24 uwlcmlps (day threshold),of 9K A equivalent light for ramps in the bandlimited range of 100 us to 2 ms an output trigger signal from comparator15 is generated. This trigger signal may be utilized to fire an electricflash system such as the prior art system hereinafter described.

The output of comparator 15 may also be applied to the base of an NPNtransistor 25 which in turn is connected to a PNP transistor 26 througha resistor 27 for use in the interlock system. Thus, the emitter oftransistor 26 receives a positive bias signal from line 101 wheninterlock circuit conducts. Dropping resistor 29 connects between theemitter and base of transistor 26 so that both transistors 25 and 26 arerendered conductive upon receiving a positive output signal fromcomparator l5 indicative that the threshold to which comparator I5 isset has been exceeded. Neither conducts in the absence of a bias signalfrom line 101 when interlock circuit 70 is non-conductive. When in thiscondition, any output from comparator 15 has no effect upon the system.7

The collector electrode of transistor 26 may be connected to a prior artspark gap trigger circuit by way of NPN transistor 30 through a resistor31 and diode 32 as shown. Transistor 30 likewise may have its collectorconnected to receive positive bias from line 101 similarly to theemitter of transistor 26. When transistor 26 becomes conductive,transistor 30 conducts supplying a signal to the gate electrode ofsilicon controlled rectifier 36 through diode 37 and resistor 38.

The prior art spark gap trigger circuit has an ac. power supply 40 thatcharges capacitor 43 through resistor 42, diode 41 and the primarywinding of transformer 45. The signal from transistor 30 renders SCR 36conductive and capacitor 43 discharges through the primary winding oftransformer 45, resistor 47 and SCR 36. This induces a high voltagetrigger pulse in the secondary winding of transformer 45.

The secondary winding of transformer connects to the trigger electrodeof spark gap 50 through capacitor 51 in spark gap circuit 52. Thetrigger electrode of spark gap 50 connects through resistor 53 to theupper main electrode of spark gap 50. The main electrodes of spark gap50 also connect in a series loop with main energy storage capacitor 56,the secondary winding of transformer 45, capacitor 51 and resistor 53.Lead 102 supplies d.c. charging voltage to main energy storage capacitor56. Resistors 53 and 54 prevent the building up of stray charges on theelectrodes of spark gap 50 prior to triggering.

The high voltage trigger pulse induced in the secondary winding oftransformer 45 is applied in series with the voltage on chargedcapacitor 56 across the lower main electrode and trigger electrode ofspark gap 50, causing spark gap 50 to ionize and become conductive.

Flash circuit 61 has two parallel branches. The series connection ofhigh voltage capacitor 62 and the primary winding of transformerconnects in parallel across resistor 54. Similarly, the seriesconnection of the main electrodes of flashtube 63 and the secondarywinding of transformer 60 connects in parallel across resistor 54. Thetrigger electrode of flashtube 63 is grounded.

When spark gap 50 becomes conductive, capacitor 56 commences to chargecapacitor 62 through the primary winding of transformer 60. Thischarging pulse induces a high voltage pulse in the secondary winding oftransformer 60 which may be on the order of 15 to 20 kilovolts peak andhave a duration on the order of one microsecond. This high voltage pulseadds in series with the voltage on capacitor 56. The sum of thesevoltages applied across the main electrodes of flashtube 63 causes thexenon gas in the flashtube to ionize. Concurrently the sum of thesevoltages is applied between the trigger electrode and the upper mainelectrode of flashtube 63 further ensuring ionization of the xenon gasin flashtube 63. As soon as ionization occurs flashtube 63 becomesconductive and main discharge capacitor 56 discharges through theflashtube producing both visible light and ultraviolet light whichactivates the photochromic material in the lenses of the goggles.

Referring now to FIG. 3 the interlock circuit comprises a microswitch 71located in a helmet (not shown) and is actuated to the closed positionwhen the helmet is worn and switches to the open position when thehelmet is removed from the head. High voltage control 73 connects toswitch 71 by means of a voltage divider circuit comprising resistors 74and 75 connected in series and grounded. Comparator 76 connects to thejunction between resistors 74 and 75. Voltage bias +V applies areference voltage to comparator 76 when microswitch 71 is closed throughresistors 74 and 75. Voltage bias -V connects to the same terminal ofcomparator 76 through resistor 77. Thus, when switch 71 is open theterminal of comparator 76 assumes negative bias and upon closure ofswitch 71 it assumes a positive bias. A negative bias on this terminalrenders comparator 76 inoperative. The other input to comparator 76 issupplied by input lead 102 from main energy storage capacitor 56 throughresistors 78 and 79, the other terminal being connected to the junctionof these resistors.

When switch 71 is open, comparator 76 is inoperative and solid staterelay 80 is open between a.c. voltage V and ac. d.c. converter 82. Thisinhibits charging of main energy storage capacitor 56. When switch 71 isclosed and capacitor 56 is charged to a predetermined value, comparator76 likewise is rendered inoperative, preventing further charging ofcapacitor 76. However, when switch 71 is closed and the voltage oncapacitor 76 is below said predetermined value comparator 76 becomesoperative, closing solid state relay 80, completing the circuit betweenac. voltage V and ac. d.c. converter 82, thus permitting capacitor 56 tocharge.

Capacitor discharge relay 83 for discharging capacitor 56 comprises coil84 and normally closed switch contacts 85 connected to capacitor 56through resistor 86 and lead 102. The discharge of capacitor 56 iscontrolled by microswitch 71 that is connected to the base of transistor90 that has its emitter grounded and whose collector is connected tocoil 91 in parallel with diode 92 of relay 93. When switch 71 is closedvoltage +V passes through coil 91 and transistor 90 closes switchcontact 94 as shown. This causes'coil 84 to be energized from voltagesupplis +V and V through switch 94 and opens switch contacts 85 asshown. On switch 71 opening the switch 94 transfers to the open positioncausing switch contacts 85 to close. Capacitor 56 thereupon dischargesto ground through resistor 86.

It will be remembered that light detector 16 can produce an outputsignal on the collector of transistor 26 only if voltage +V is availableon line 101. Thus, when switch 71 is open, there is no signal output atlight de tector 16.

The operation of the device will now be explained with reference to theFIGURES. It is assumed power is being supplied to the system andmicroswitch 71 is closed. If photodiodes ll sense the ambient light ofdaytime voltage, comparator 12 is actuated setting voltage comparator 15at a predetermined level. If the diodes 11 sense that it is nighttime,voltage comparator 12 is not actuated and the level of voltagecomparator 15 is set by the signal +V, through resistor 17. On diodes 11sensing a rapid increase in light, a signal sent to voltage comparator15 through differentiator 13 causes an output signal from voltagecomparator 15 to be applied to the base of transistor 25 causingtransistor 25 to conduct. 1f the helmet is being worn a signal is thenreceived on lead 101 and a voltage drop developed acros's resistor 29renders transistor 26 condcutive. This, in, turn, turns on transistor 30which supplies a signal to fire SCR 36. The firing of SCR 36 causescapacitor 43 to discharge through the primary of transformer 45. Thehigh voltage pulse induced in the secondary of transformer 45 tiresspark gap 50 rendering it conductive. Capacitor S6 furnishes a chargingpulse through the primary winding of transformer 60 to charge capacitor62. This induces a high voltage pulse in the secondary winding oftransformer 60. The sum of this high voltage pulse and the voltage oncapacitor 56 is applied to the electrodes of flashtube 63 causing thexenon gas therein to ionize. When ionization occurs capacitor 56discharges through flashtube 63 producing visible light and ultravioletlight. This ultraviolet light activates the photochromic material, andin a manner of speaking closes the goggles. Photochromic activation fromelectric flash tubes is well known to those skilled in the art.

There has therefore been disclosed apparatus for automatically operatingat different threshold levels for day and night to prevent flashblindness during either. The apparatus further has an interlock systemthat protects against high voltages when operation of the apparatus isnot necessary.

It will be understood that various changes in the details, materials,steps and arrangements of parts, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby thse skilled in the art without departing from the spirit of theinvention or the scope of the following claims.

What is claimed is:

1. An automatic sensitivty adjustment system for night and day operationcomprising:

light-sensitive detector sensors for providing an output signalindicative of the light received;

first comparator means for comparing said sensors output signal with apredetermined signal and providing an output signal if said ensorsoutput signal is larger than said predetermined signal; sensors 3differentiator connected to receive said sensors output signal forproviding an output signal that is indicative of the rate of change ofsaid sensors output signal;

first signal means connected to receive said first comparator meansoutput for providing a first signal level in the presence of said firstcomparator means output signal and a second signal level in the absenceof said first comparator means output signal; and

second comparator means connected to receive said first signal meansoutput signal and said differentiator output signal for providing anoutput signal when said differentiator output signal is largerthan saidfirst signal means output signal.

2. An automatic sensitivity adjustment system according to claim 1wherein said light-sensitive detector sensors include a pair of photodiodes connected in parallel.

3. An automatic sensitivity adjustment system according to claim 2further comprising:

interlock system means connected to said second comparator means forinhibiting an output signal when said automatic sensitivity adjustmentsystem is not in use.

4. ln flashblindness protective apparatus having photochromic gogglesactivated by ultraviolet light produced by operation of an electricflash system having a main energy storage capacitor that is charged andthen discharged through an electric flashtube to produce the ultravioletlight, the improvement for daytime and nighttime operation comprising:

light-sensitive detectors for providingan output signal indicative ofambient light levels and transient changes in light intensities;

first comparator means for comparing that portion of the detectorssignal indicative of the ambient light level with a predetermined signaland providing an output signal if said portion of the detectors signalexceeds the predetermined signal;

a differentiator connected to receive the detectors output signal forproviding output signals indicative of the rates of change of thoseportions of the detectors output signal indicative of transient changesin light intensities;

first signal means connected to receive the output signal from the firstcomparator means for providing a first signal level in the presence ofan output signal from the first comparator means and a second signallevel in the absence of an output signal from the first comparatormeans;

said second comparator means connected to receive the output signallevel from the first signal means and the output signals from thedifferentiator for providing output signals when the output signals fromthe differentiator exceed the output signal levels from the first signalmeans; and

means connecting the second comparator means to the electric flashsystem for actuating the electric flash system in the presence of anoutput signal from the second comparator.

5. The improvement as in claim 4 in which the predetermined signal isset at a threshold level corresponding to the ambient light level fordaytime operation.

6. The improvement as in claim 5 in which:

the first signal level from the first signal means corresponds todaytime operation; and

the second signal level from the first signal means corresponds tonighttime operation.

7. The improvement as in claim 6 in which the first signal means furthercomprises a predetermined voltage source for providing the second signallevel. i 8. The improvement as in claim 4 further comprising interlockcircuit means connected to the second comparator means for inhibiting anoutput signal therefrom when the apparatus is not in use.

9. The improvement as in claim 8 in which the interlock circuit meansfurther comprises means for inhibiting charging of the main energystorage capacitor.

10. The improvement as in claim 9 in which the interlock circuit meansfurther comprises means for discharging the main energy storagecapacitor when the

1. An automatic sensitivty adjustment system for night and day operationcomprising: light-sensitive detector sensors for providing an outputsignal indicative of the light received; first comparator means forcomparing said sensors output signal with a predetermined signal andproviding an output signal if said ensors output signal is larger thansaid predetermined signal; sensors a differentiator connected to receivesaid sensors output signal for providing an output signal that isindicative of the rate of change of said sensors output signal; firstsignal means connected to receive said first comparator means output forproviding a first signal level in the presence of said first comparatormeans output signal and a second signal level in the absence of saidfirst comparator means output signal; and second comparator meansconnected to receive said first signal means output signal and saiddifferentiator output signal for providing an output signal when saiddifferentiator output signal is larger than said first signal meansoutput signal.
 2. An automatic sensitivity adjustment system accordingto claim 1 wherein said light-sensitive detector sensors include a pairof photo diodes connected in parallel.
 3. An automatic sensitivityadjustment system according to claim 2 further comprising: interlocksystem means connected to said second comparator means for inhibiting anoutput signal when said automatic sensitivity adjustment system is notin use.
 4. In flashblindness protective apparatus having photochromicgoggles activated by ultraviolet light produced by operation of anelectric flash system having a main energy storage capacitor that ischarged and then discharged through an electric flashtube to produce theultraviolet light, the improvement for daytime and nighttime operationcomprising: light-sensitive detectors for providing an output signalindicative of ambient light levels and transient changes in lightintensities; first comparator means for comparing that portion of thedetectors'' signal indicative of the ambient light level with apredetermined signal and providing an output signal if said portion ofthe detectors'' signal exceeds the predetermined signal; adifferentiator connected to receive the detectors'' output signal forproviding output signals indicative of the rates of change of thoseportions of the detectors'' output signal indicative of transientchanges in light intensities; first signal means connected to receivethe output signal from the first comparator means for providing a firstsignal level in the presence of an output signal from the firstcomparator means and a second signal level in the absence of an outputsignal from the first comparator means; said second comparator meansconnected to receive the output signal level from the first signal meansand the output signals from the differentiator for providing outputsignals when the output signals from the differentiator exceed theoutput signal levels from the first signal means; and means connectingthe second comparator means to the electric flash system for actuatingthe electric flash system in the presence of an output signal from thesecond comparator.
 5. The improvement as in claim 4 in which thepredetermined signal is set at a threshold level corresponding to tHeambient light level for daytime operation.
 6. The improvement as inclaim 5 in which: the first signal level from the first signal meanscorresponds to daytime operation; and the second signal level from thefirst signal means corresponds to nighttime operation.
 7. Theimprovement as in claim 6 in which the first signal means furthercomprises a predetermined voltage source for providing the second signallevel.
 8. The improvement as in claim 4 further comprising interlockcircuit means connected to the second comparator means for inhibiting anoutput signal therefrom when the apparatus is not in use.
 9. Theimprovement as in claim 8 in which the interlock circuit means furthercomprises means for inhibiting charging of the main energy storagecapacitor.
 10. The improvement as in claim 9 in which the interlockcircuit means further comprises means for discharging the main energystorage capacitor when the apparatus is not in use.